Activation of metallocene hydride intermediates by methylaluminoxane in alkene dimerization and oligomerization

In order to elucidate the dependence of the structure and reactivity of the bimetallic hydride intermediates formed in the systems metallocene-organoaluminum compound-activator on the nature of the transition metal atom and ligand environment, we used NMR spectroscopy to study reactions of a series of L2MCl2 complexes (M = Hf, Zr; L2 = Cp2, (CpMe)2, ansa-(Me2C)2Cp2, ansa-Me2CInd2) with HAlBui2 and MMAO-12 activator. As a result, M, Al-bimetallic intermediates containing [L2MH3] and [(L2M)2H3] type moieties were detected for both hafnium and zirconium complexes with cyclopentadienyl ligands. The [L2ZrH3] type structure predominates in the system based on the ansa-bis-indenyl zirconium complex. The detected complexes provide associates with MMAO-12 [L2MH3]center dot MAO and [(L2M)2H3]center dot MAO. The MAO-associated intermediates of the [(L2M)2H3] type are precursors of the catalytically active sites for alkene dimerization. In the system based on ansa-bis-indenyl zirconium complex, the intermediate of the [L2MH3] type affords a set of hydride structures, presumably cationic, which lead to alkene oligomerization.

Automated summary

By using NMR spectroscopy, it was found that different bimetallic hydride intermediates were formed in the reactions of vanadium and zirconium complexes with HAlBui2 and MMAO-12 activator. The zirconium complexes tended to form [L2ZrH3] structures, and the vanadium and zirconium complexes formed complexes with MMAO-12. These complexes served as precursors for the catalytically active sites for alkene dimerization and oligomerization reactions.